Control and measuring system for high voltage electric power transmission systems



3.460,042 13 ELECTRIC R. H. HARNER Aug. 5, 1969 CONTROL AND MEIASURINGSYSTEM FOR HIGH VOLTAG POWER TRANSMISSION SYSTEMS 8 Sheets-Sheet 1 FiledOct. 20, 1965 R. H. HARNER 3,460,042 CONTROL AND MEASURING SYSTEM FORHIGH VOLTAGE ELECTRIC Aug. 5, 1969 POWER TRANSMISSION SYSTEMS Filed Oct.20. 1965 8 Sheets"-Sheet 2 Aug. 5, 1969 R. H. HARNER .04

CONTROL AND MEASURING SYSTEM FOR HIGH VOLTAGE ELECTRIC 7 POWERTRANSMISSION SYSTEMS Filed Oct. 20, 1955 8 Sheets-Sheel 5 R. H. HARNER3,460,042

TAGE ELECTRIC Aug. 5. 1969 CONTROL AND MEASURING SYSTEM FOR HIGH VOLPOWER TRANSMISSION SYSTEMS 8 Sheets-Sheet 4 Filed Oct. 20. 1965 m w mFZDIm 20mu F2umm30 msm R. H. HARNER 3,460,042 CONTROL AND MEASURINGSYSTEM FOR HIGH VOLTAGE ELECTRIC POWER TRANSMISSION SYSTEMS Filed Oct.20, 1955 8 Sheets-Sheet 5' 5, 1969 R. H. HARNER 460,042

CONTROL AND MEASURING SYSTEM FOR HIGH VOLIAGE ELECTRIC POWERTRANSMISSION SYSTEMS Filed Oct. 20, 1965 8 Sheets-Sheet e I L F.AMPLIFIER 48 LIMITER l CRYSTAL FILTER Z l l L- Aug. 5, 1969 R. H. HARNER3,460,0

CONTROL AND MEASURING SYSTEM FOR HIGH VOLTAGE ELECTRIC POWERTRANSMISSION SYSTEMS Filed Oct. 20. 1965 8 Sheets-Sheet 7 CRYSTAL FILTERLOW BAND PASS PASS FILTER TO RELAYS OR AMPLFIER 3,460,042 CTRIC Aug. 5,1969 R. H. HARNER CONTROL AND MEASURING SYSTEM FOR HIGH VOLTAGE ELEPOWER TRANSMISSION SYSTEMS Filed Oct. 20. 1965 8 Sheets-Sheet 8 2 A7I.!II..IIIIJ mu nsoomo 3,460,042 CONTROL AND MEASURING SYSTEM FOR HIGHVOLTAGE ELECTRIC POWER TRANSMSSION SYSTEMS Robert H. Harner, Park Ridge,Ill., assignor to S & C Electric Company, Chicago, Ill., a corporationof Delaware Filed Oct. 20, 1965, Ser. No. 498,696 int. Cl. H04b 1/02,1/04 U.S. Cl. 32567 21 Claims ABSTRACT OF THE DISCLOSURE A radiotransmitter is modulated in accordance with a variable of a high voltageconductor at its potential to transmit a corresponding signal to areceiver at ground potential.

This invention relatos, generally, to remote current measuring andcircuit breaker control in connection with high voltage alternating anddirect current electric power transmission systems operating at voltagesranging from 138 kv. to 750 kv. but it is not limited to this voltagerange. It constitutes an improvement over the system disclosed inapplication Ser. No. 279,376, filed May 10, 1963.

Among the objects of this invention are: To provide in a new andimproved manner for transmitting a signal corresponding to the magnitudeof a variable at the potential of a high voltage conductor and forreceiving the signal at ground potential; to employ for this purpose aradio transmitter operating at the potential of the conductor and aradio receiver operating substantally at ground potential; to providesuch a radio transmitter that is free from the effects ofelectromagnetic and electrostatic fields in the ambient of the highvoltage conductor and adjacent high voltage conductors, and i free frominterference by man made and natural causes; to construct the radiotransmitter such that it does not generate corona; to operativelyconnect the receiver to the means intended to be responsive to thesignal received thereby from the transmitter only when such a signal isbeing received; to employ a frequency modulated transmitter and receivercombination for making the measurement and transmitting and receiving itwith the receiver being operatively connected to signal responsive meansonly when the transmitter is operating substantially at centerfrequency; to provide a receive capable of operating at low fieldstrength and in a noisy environment that usually exists in a typicalelectric power station; to transmit and receive the signal correspondingto current flow in the conductor; to employ for the frequency modulatedtransmitter a voltage controlled crystal oscillator the frequency ofwhich is varied as a function of the magnitude of the current flow inthe conductor; to arrange a crystal controlled frequency modulatedreceiver to generate a voltage that is instantaneously proportional tothe current flow in the conductor; to multiply the frequency generatedby the crystal oscillator of the transmitter and to radiate it asfrequency modulated by the niodulating voltage which varies according tothe current flow in the conductor; to modulate a radio transmitteroperating at the potential of a high voltage electric power transmissionline or conductor by a voltage derived therefrom due to line currentflow through a resistive tubular conductor, the voltage drop across theconductor varying as a function of such current flow; to position theradio transmitter within such a resistive tubular conductor; to combinewith the resistive tubular conductor metallic end cap means whichfunction therewith to electrostatically and electromagneti cally sheldthe transmitter and minimize the emission of atent 3,4-6,@42 PatentedAug. 5, 1969 corona at the potential of the line; to enclose theresistive tubular conductor by an outer coaxial and coextensive highconductivity tubular conductor connected in series therewith; tointerconnect the radio transmitter and the end cap means so that thelatter function as the antenna for the former; to obtain the modulatingvoltage for the transmitter from a non-inductive shunt; to limit thesignal input to the transmitter to a predetermined value regardless ofthe magnitude of the variable, such as current flow, above apredetermined value; to energize the frequency modulated transmitter byvoltage derived from current flow in the conductor only when thatvoltage is at a predetermined value; to arrange for a power supply atconstant voltage for the transmitter from the conductor in which thecurrent flow may vary from 50 to 100,000 amperes; to regulate thisvoltage to maintain it substantially at this predetermined value tomaintain the operation of the frequency modulated transmitter inresponse to predetermined current flow in the conductor, therebyeliminating need for batteries; and to provide a feedbacktransconductance amplifier, to drive a particular meter, relay or otherresponsive device, capable of causing a current flow to a burden or loadcircuit which current flow is independent of the impedance of the burdenor load circuit over a wide range of impedance.

In the drawings:

FIG. 1 shows diagrammatically a circuit breaker control and currentmeasuring system for high voltage electric power transmission systemsembodyng this invention, it being understood that duplicate equipment isprovided for each of the other phases of a poiyphase alternating currenttransmission system.

FIG. 2 is a vertical sectional view of a coaxial shunt that is connectedin the high voltage transmission line.

FIG. 3 is a top plan view of the coaxial shunt shown in FIG. 2.

FIG. 4 shows the circuit connections for the power supply circuit forthe frequency modulated transmitter located in the coaxial shunt.

FIG. 5 shows the circuit connections for the frequency modulatedtransmitter located in the coaxial shunt.

FIGS. 6, 7 and 8, placed in side-by-side relation in the order named,show the circuit connections for the frequency modulation receiver.

FIG. 9 shows the circuit connections for the trans-conductance feedbackamplifier.

Referring to FIG. l, the reference character 10 designates a highvoltage electric power transmission line or conductor which is insulatedby suitable insulation from ground. It is arranged to operate atvoltages ranging upwardly to 750 kv. or higher. The conductor 10comprises one phase of a polyphase altemating current system. Wheredirect current is used, it comprises the ungrounded conductor.

It is desirable to provide for measuring the current flow in theconductor 10 for metering purposes and also for controlling theoperation of a circuit breaker, such as the circuit interrupterindicated, generally, at 11 the contents of which are connected in theconductor 10 for completing the circuit therethrough. The circuitinterrupter lll can be of conventional construction. The trippingarrangement for the circuit interrupter 11 is illustrateddiagrammatically. It includes a trip coil 12 that is arranged to beenergzed from a suitable source, such as a battery 13 on closure ofcontacts 14 of an overcurrent relay 15. The relay 15 may be aconventional inverse time current relay that is provided with anoperating winding 16. A static relay can be used. Also provision can bemade for reclosing the circuit interrupter 11 subsequent to operating ofthe relay 15 for tripping it.

It is desirable to provide for measuring the current flow in theconductor and for this purpose a current responsive device indicated at17 is employed. The current responsive device 17 may be an ammeter, acurrent element of a wattmeter, the current element of a watthour meter,the current element of a power factor meter, a recording oscillograph,etc.

Ordinarily a number of windings 16 and current responsive devices 17 areconnected for energizaton in series circuit relation. The impedance ofthese circuits may vary depending upon the operating characteristics ofthe particular devices. While it is desirable that provision be made foroperating them in accordance with or on predetermined current flow, inview of the varyng impedance of the respective circuits, it is desirablethat provision be made for maintaining at a constant value the measuredcurrent flow in such manner that it is independent of the varyingimpedance. For this purpose there is provided an amplifier that isindicated, generally, at IS. This may be a transconductance feedbackamplifier. Other signal conditioning devices can be employed also. Forvoltage responsive devices the output from the receiver, to bedescribed, can be used directly or amplified to appear as a voltagesource.

For measuring the current flow in the conductor 10 there is provided acoaxial shunt that is indicated, generally, at 20 It includes an innertubular conductor 21 of an appropriate metal which forms a resistivesection for a purpose to be described. The inner tubular conductor 21 isconnected by a lower terminal plate 22 to an outer tubu lar conductor 23that is coaxially related thereto and coextensive therewith and isformed preferably of a high conductivity material. A floating groundconnection to the coaxial shunt 20 is indicated at 24.

Within the coaxial shunt 20 there is located a frequency modulated radiotransmitter which is indicated, generally, at 25. It includes a crystalcontrolled frequency modulated oscillator 26 which is connected bycoaxial conductors 27 and 28 to metallic end caps 29 and 30 located atthe ends of the outer tubular conductor 23. The metallic end caps 29 and30 provide the antenna for the transmitter 25. They are of such size andshape as to resonate at the frequency of the crystal controlledfrequency modulated oscillator 26. In addition the metallic end caps 29and 30 together with the inner and outer tubular conductors 21 and 23effectively shield the radio transmitter 25 and provide a configurationfrom which the emission of corona at the.

potential of the conductor 10 is minimized. The construction of thecoaxial shunt 20 is such that it not only minimizes corona emission butalso it shields the transmitter 25 from the effects of the relativelystrong electromagnetic field generated by high or short circuit currentflow in the conductor 10. The net magnetic field within the innertubular conductor 21 is practically zero for any current flow inconductor 10.

The radio transmitter 25 includes a modulation control 31 which isconnected by conductors 32 and 33 to spaced points 34 and 35 along theinner tubular conductor 21 between which a voltage drop appears that isa linear function of the magnitude of the current flow in the conductor10. The modulation control 31 provides selectable or variable modulationsensitivities to, in essence, change the transformation ratio of thesystem at any level over the dynamic range of the system such as 50 to10,000 amperes; 200 to 40,000 amperes, 400 to 80,000 amperes, etc., Alsothe modulation control 31 makes possible limitation of the maximumfrequency deviation of the system to various levels such as not toexceed the band pass of the receiver. Instead of a linear relationshipbetween bus current and frequency deviation being used, a logarithmicfunction can be employed to increase the effective range.

For energizing the radio transmitter 25 a power supply 36 is employedfor energization as the result of current flow in the conductor 10.Other sources of energy can be employed such as a battery, solar cells,etc., particularly when flow of direct current in the conductor 10 is tobe measured and a corresponding signal transmitted.

In accordance with this embodiment of the invention the power supply 36is arranged to limit the voltage applied to the radio transmitter 25.The power supply 36 is c nnected for energization to the conductor 10 bya transformer that is indicated, generally, at 37 and located within themetallic end rap 29 If desired, it can be located exteriorly to the endcap 29. The transformer 37 employs the conductor 10 as a single turnprimary winding. The conductor 10 extends through a saturable magneticcore 38 for the purpose of limiting the induction of current in asecondary winding 39 on the core 38. The saturable core 38 is employedsince it is likely that the conductor 10 will have a relatively highcurrent flow therein greatly in excess of normal load current flow. Suchexcess current flow takes place under fault conditions and, except forthe saturable characteristic of the core 38 and the following limiter,would induce an unusually high voltage in the secondary winding 39. Thecore 38 also has relatively high induction at low levels of current flowin conductor 10, so that an adequate voltage and power output areavailable at low current flow in the conductor 10.

Since the frequency at which the frequency modulated transmitter 25functions is affected by the voltage from the power supply 36 there isprovided, as described hereinafter, a voltage responsive device andregulator in the power supply 36. The device energizes the transmitteronly upon the application of an adequate voltage. This voltage is suchthat the frequency modulated oscillator 26 will function substantiallyat its center frequency when turned on and thus will not transmit animproperly modulated carrier. Provision is made for turning on the powersupply 36 to energize the oscillator 26 only When a properly filteredand regulated voltage is available for this purpose. Current flow inconductor 10 must be above a certain threshold for this to happen, Asupply voltage with a high ripple would be undesirable since it wouldappear as a effective modulation of the carrier.

The frequency modulated signal radiated from the antenna formed by theend caps 29 and 30 is picked up by an antenna 42 of a frequencymodulaton receiver that is indicated, generally, at 43 and also isindicated as being grounded at 44. Since there is not direct connectionbetween the conductor 10 or any part associated therewith and thereceiver 43, it is possible to take advantage of the insulation normallyprovided for the conductor 10 and it is not necessary to provide anyother insulation for the transmitter 25 or receiver 43 which, as pointedout, is arranged and adapted to operate at ground potential. The systemfunctions entirely independently of the potential of the conductor 10with respect to ground or other conductors. Thus, it may be applied to apower system operating at any voltage. The circuit details of thereceiver 43 will be set forth hereinafter. For present purposesreference is made to the diagrammatic showing in FIG. l. The incomingsignal from the antenna 42 is fed to a radio frequency, double turnedamplifier and mixer 45 with which there is provided a tunable crystaloscillator 46. The output of the crystal oscillator 46 beats with thereceived frequency modulated signal in the mixer to provide anintermediate frequency which is applied to a crystal filter 47 forremoving, in part, extraneous frequencies consisting of interferingtransmissions, internally generated receiver noise, and impulse andatmospherc noise. The output of the crystal filter 47 is applied to anintermediate frequency amplfier and limiter 48. Another crystal filter49 is employed between the intermediate frequency amplifier and limiter38 and the demodulator and squelch 50 for the purpose of furtherexcluding extraneous frequencies and noise. The output of thedemodulator and squelch 50 is a voltage that is instantaneouslyproportional to the current flow in the conductor 10. This voltage isapplied to a low pass filter 51 for further removing extraneous signalsand then is amplified by output amplifier 52. While the output of thereceiver 43 can be employed for metering and relaying purposes, thesignal is relatively weak. Accordingly, another amplifier 18, forexample a transconductance feedback amplifier, can be employed not onlyfor amplifying the voltage which varies according to the current flow inthe conductor but also to accommodate load circuits or burdens havingvarying impedances but requiring for their proper operation the flow ofpredetermined current. A voltage amplifier can be used in connectionwith the output of amplifier 52 to drive voltage dependent loads.

FIGS. 2 and 3 show the details of construction of the coaxial shunt 20.The terminal 55, preferably of a high conductivity material, is employedhaving a terminal pad 56 to facilitate connection in the conductor 10.The other end of the terminal 55 is suitably connected to a collectorring 57 that is secured to the upper end of the outer tubular conductor23 for evenly distributing current intoit. An insulating ring 58 isinterposed between the upper ends of the inner and outer tubularconductors 21 and 23 to maintain them in predetermined coaxial spacedrelation. An upper terminal plate 59 of good conducting material isconnected to the upper end of the inner tubular conductor 21 and it isconnected by a terminal 60, preferably a high conductivity material,which has a terminal pad 61 to facilitate the connection to conductor10. The terminal 60 extends through a suitable opening 62 in the uppermetallic end cap 29. Insulating rings 63 at the upper and lower ends ofthe outer tubular conductor 23 serve to insulate the end caps 29 and 30therefrom. Insulating bolts extend through the lower terminal plate 22and the upper terminal plate 59 and serve to hold them in spacedassembled relation and in good contact engagement with the upper andlower ends of the inner tubular conductor 21. A heat sink plate 65 isprovided for mounting the radio transmitter 25 thereon It is locatedbetween insulating support plates 66 which are carried by the tie bolts64. By locating the radio transmitter 25 within the inner tubularconductor 21, it is electromagnetcally and electrostatcally shieldedwith respect to its own and adjacent high power and high voltagecircuits.

FIG. 4 shows the circuit connections for the power supply 36. Here theconductor 10 is shown as the primary winding for the transformer 37 withthe secondary winding 39 located on the saturable core 38. Typical loadcurrent rating of the conductor 10 ranges from 600 to 2,000 amperes.When the current flow is less than about 50 amperes there is noparticular need for an output for relaying applications and manymetering applications. Accordingly, the size of the core 38 and itscharacteristics were selected so that a regulated output voltage ofabout 12 volts is provided by the power supply 36 on flow of 50 amperesor more in the conductor 10. The core 38 is fabricated of a nickel-ironalloy which exhibits high permeability at very low magnetizing force,and saturates at a relatively low flux density. High flux density at lowmagnetizng force is necessary to produce adequate voltage and poweroutput at low values of line current. A permeability of approximately100,000 at a flux density of 2,0004,000 gauss and a magnetizing torce of.02.04 oersted produces the desired result. Saturation of the core at aflux density of approximately 6,0008,000 gauss eiectively limits outputvoltage and power from the transformer secondary to a level within thepower handling capability of the limiting and filtering circuits at linecurrents up to 100,000 amperes or more under fault conditions. Since thecore is driven into extreme saturation the untiltered and unregulatedtransformer secondary output is extremely distorted. Provision is madefor rectifying, filtering and regulating the output of the secondarywinding 39. For this purpose there is provided a full wave rectifier 71of the bridge type. The output of the rectifier 71 is applied to afilter and limiter circuit 72 which includes a capacitor 73,

series connected Zener diodes 74 and a regulating resistor 75. The Zenerdiodes 74 are arranged to break down on application thereto of a givenvoltage thereby together with the resistor 75 limiting the voltage thatcan be applied to the voltage regulator 76. The capacitance of thecapacitor 73 in conjunction with the impedance of the secondary winding39 provides a suitable RC time constant for the power supply 36 and thecombination of the capacitor 73 and the Zener diodes 74 controls theripple in the output from the rectifier 71 that is within the range ofthe regulator 76 to accommodate and remove. The voltage regulator 76 isarranged to have an extremely good regulation and low ripple output overthe entire range of current flow likely to take place in the conductor10. This is of extreme importance since the frequency of the crystalcontrolled frequency modulated transmitter 26 is dependent upon thevoltage of its supply and can be maintained substantially at the desiredcenter frequency only when the supply voltage is regulated to within thelimits mentioned. As pointed out, by substantially eliminating theripple voltage, a constant voltage is provided for energizing theoscillator 26 without applying extraneous modulation to the carrierfrequency. This is the effect that could be obtained through the use ofa battery source which is impractical under these circumstances due toinaccessibility and problems in maintaining the battery fully charged.

The output voltage of the regulator 76 can be varied by a potentometer77. This adjustment provides for a variation in the output voltage of or10% and allows coarse tuning of the transmitter to receiver frequency.

As pointed out, it is desirable that the power supply 36 initiate the-functioning of the crystal controlled frequency modulated transmitter25 only when the energiz ing voltage therefor is at a predeterminedvalue. Also it is necessary that transmission begin within a fewmilliseconds after initiation of current flow in the conductor 1G. Thetransient response of the transformer 37 and associated elements of thepower supply 36 is such that the required power for the oscillator 26 isavailable within a few milliseconds. In order to insure that thetransmitter functions only under the proper operating conditions,normally open contacts 79 are provided in the output circuit from thevoltage regulator 76. The contacts 79 form a part of a voltageresponsive relay having an energizer winding 80 that is connectedthrough a variable resistor 81 and across the terminals of the filterand limiter circuit 72. The voltage responsive relay employing thecontacts 79 and winding 80 can be a sensitive, high speed, bounce-freeswitching device, such as a reed switch. If desired, a solid stateswitch can be employed to perform the switching function which connectsthe output of the voltage regulator 76 to energize the crystalcontrolled frequency modulated transmitter 25 at the proper instant.

When the current flow in conductor 10 drops below the threshold value,the winding 80 is deenergized suficiently to permit opening of contacts79. Until they open, the voltage regulator 76 maintains the constantdirect voltage to the oscillator 26, thereby holding it at the centerfrequency until the contacts 79 are opened.

FIG. 5 shows in detail the circuit connections employed for themodulation control 31 and the crystal controlled frequency modulatedoscillator 26. It will be recallcd that the conductors 32 and 33 areconnected to spaced points 34 and 35 along the inner tubular conductor21 where a voltage drop appears that is directly proportional to and inphase with the current flow in the conductor 10. Since the coaxial shuntassembly is substantially noninductive, this voltage drop is in phasewith the current flow in the conductor 10. If that cur rent flow is adirect current rather than an alternating current, then this voltagedrop is a direct function of the magnitude of the current flow in theconductor 10. The input from the coaxial shunt 20 is applied overconductors 32 and 33 to modulate input control 31 which comprises anetwork of resistors 82 the connections to which can be varied toprovide the desired voltage for application to a voltage controlledcrystal oscillator 83. This voltage is limited by clipping Zene diodes84 which are connected such that, regardless of the maguitude of thecurrent flow in conductor 10, the voltage applied to the crystaloscillator 83 does not cause it to transmit a signal to the receiver 43of such magnitude as to cause it to tend to operate beyond its pass bandand thus provide an erroneus signal.

It will be understood that the frequency of the voltage controlledcrystal oscillator 83 is a sub-hamonic of the center frequency of thecrystal controlled frequency modulated transmitter 25 which is radiatedto the antenna 42 of receiver 43. The oscillator output frequency isvaried as a function of the analog voltage applied thereto from themodulation input control 31 which varies accord ing to the magnitude ofthe current flow in the conductor 10. Associated with the oscillator 83is a driver 87 and a tripler 88 which multiplies the frequency generatedby the oscillator 83 to provide the transmission frequency which isfrequency modulated for example or 100 ke. over the range of maximumcurrent flow in the conductor 10. This band Width should be relativelynarrow With respect to the spacing of stations or interferng signals inthe frequency bands being used. This makes the system of the presentinvention readily applicable with the center frequency of thetransmitter being chosen to lie somewhere between the center frequenciesof adjacent commercial frequency modulated broadcast stations when thisfrequency band is chosen. The frequency deviation of the crystalcontrolled frequency modulated transmitter 26 is proportional to currentflow in conductor to Within at least or l% up to full modulation.

An output circuit 89 is associated With the tripler 88. It includes acoupling transformer 90 having a primary Winding 91 energized from thetripler 88 and a secondary winding 92 having a center tap 93 which isgrounded as indicated. The output of the secondary Winding 92 is appliedto an antenna coupling circuit 97 and thence by conductors 27 and 28 tothe metallic end caps 29 and 30 which function as the antenna for thepurpose of radiating the frequency modulated transmission signals. Theoutput power of the transmitter 25 may be higher than required undersome conditions and the antenna coupling circuit 97 is arranged toattenuate the signal. The secondary winding 92 offers a relatively highimpedance to the carrier frequency from the oscillator 26 and arelatively low impedance to the normal power frequency of the conductor10. Thus, the end caps 29 and 30 are maintained substantially at thesame potential and at the potential of the conductor 10.

The construction of the voltage controlled crystal oscillator 26 is suchthat it is operating at center frequency within one millisecond afterclosure of contacts 79 and thereby energization from the power supply36.

Other voltage analog signals can be fed into the modulation inputcontrol 31. For example, if a signal corresponding to the potentonal ofthe conductor 10 is to be transmitted, then an analog of this potentialis applied to conductors 32 and 33. In a similar manner stressvariations in the conductor 10 or vibration thereof can be converted toanalog voltages and used to pull the oscillator 83, Also a subcarrierfrequency can be modulated by the analog voltage of a variable and thecorresponding signal used to modulate the carrier frequency of thetransmitter 25.

FIGS. 6, 7 and 8 show the detailed circuit connections for the frequencymodulated receiver 43 The receiver 43 is arranged for battery operationand crystal frequency control. It employs principally solid statedevices and crcuitry to provide maximum sensitivity, selectivity andminirnum impulse noise disturbance. The high sensitivity is requiredsince the available field strengths may be limited depending upon thefrequency band selected. Accordingly, the receiver 43 is arranged tooperate satisfactorily at a field strength of the order of 50 microvoltsper meter. Employing the circuit connections disclosed herein arelatively low noise figure for the radio frequency tuner is obtained.

It is contemplated that the system of the present invention may operateon transmission frequences adjacent to relatively strong commercialbroadcast stations. Accordingly, the receiver 43 must have a high degreeof selectivity in order to avoid interference with commercial stationsand the reception of false signals. For this purpose the amplifier andmixer 45 includes a radio frequency double tuned amplifier 100.Associated with the amplifier is the tunable crystal oscillator 46 whichgenerates a frequency that is applied to a mixer 101 and beats with thefrequency modulated signal from the amplifier 100 to generate anintermediate frequency signal which is carried by a coaxial conductor102 to the crystal filter 47, FIG. 7. The crystal control in thereceiver 43 is employed to provide a fixed frequency reference base.Thus the system is unlikely to drift as a result of temperature changeas would a system solely using tuned LC circuits.

The crystal filter 47 is designed to provide high attenuation forfrequencies outside its pass band while providing uniform responsewithin the pass band with little insertion loss. Here the crystal filter47 is a restricted band pass crystal filter which is based on theproximity of an interfering commercial frequency modulated broadcaststation and its field strength. The compromise is made between a maximumband Width required for good impulse noise performance and a relativelynarrow band Width for good selectivity. These considerations are ofpartcu lar importance in areas having a high density of commercialfrequency modulated broadcast stations and high ambient impulse noise inthe form of corona and arcing. Further improvement in selectivity can beobtained by using vertical polarzation for the transmitter 25 ratherthan horizontal polarization, depending upon the polarization of theadjacent commercial frequency modulated broadcast station or otherinterfering signal.

The output from the crystal filter 47 is applied to an intermediatefrequency amplifier 103 which forms a part of the amplifier and limiter48. Associated with the intermediate frequency amplifier 103 is alimiter 104 that is employed to remove the amplitude modulated componentof the received signal. The amplifier and limiter 48 are provided withan automatic gain control detector 105 which is connected by conductor106 to the double tuned amplifier 100 shown in FIG. 6. The automaticgain control detector 105 also is connected to an automatic gain controlamplifier 107 which has associated there with a signal strengthindicator 108, A switch 169 is employed in the indicator 108 forcontrolling the connection of an indicating meter 110 to the automaticgain control amplifier 107 for the purpose of occasonally determiningthe strength of the signal that is being received and for checkingsystem operation. As shown in FIG. 8 a coaxial conductor 113interconnects the limiter 104 with a second crystal filter 49 thefunction of which is to further remove noise frequencies generated inthe intermediate frequency amplifier 103 and limiter 104 due to limitingaction. The band pass of the crystal filter 49 must be lower than thatof the crystal filter 47 and the filter center frequency must besymmetrical about the center frequency for good noise performance. Theoutput of the crystal filter 49 is applied to a demodulator 114 which isconnected by a conductor 115 to the tuning and signal strength indicator108 shown in FIG. 7. The demodulator 114 is arranged to generate acrossa potentiometer 116 a voltage Which corresponds instantaneously inmagnitude and phase with the current flow in the conductor 10. Theoutput level of the demodulator 114 as represented across thepotentiometer 116 is applied over a conductor 118 for furtheramplification to be described. Response of the receiver 43 to the suddensensing of a carrier signal, due to the transmitter 25 becoming operablewhen the current in conductor or the bus current rises above thethreshold level, is a critical part of the system. The squelch circuitdesign and receiver transient response must be such that no unwantedtransients appear in the output of the receiver 43 due to the suddentappearance of a carrier signal. The receiver output must contain onlythose transients in the sensed bus current and not those generated inthe receiver 43. The radio frequency amplifier tuned circuits 45, IFamplifier tuned circuits 48, demodulator circuits 50, and the filtersmust yield a balanced or zero output when no carrier is present and onlyambient noise is being received. The output must also be balanced aboutzero with no DC offset when the carrier is suddenly received. Theserequirements necesstate careful adjustment and stability of all thesecomponents so that the noise balance and carrier frequency balance ofthe receiver 43 remain fixed.

It is desirable, when the current in conductor 10' increases so as tocross the 50 ampere threshold turn on level for the radio transmitter25, that there be a slight time delay in the application of the voltageapplied to the circuits to be controlled thereby in order to ensure thatthe crystal controlled frequency modulated transmitter 25 is operatingsubstantially at the center frequency and that a reliable signal isobtained. For this purpose a squelch circuit 119 is employed. It isconnected by conductor 120 to the automatic gain control amplifier 107.The squelch circuit 119 includes a relay that is indicated, generally,at 121 and has an operating winding 122 and normally open contacts 123.The contacts 123 are arranged to be closed a short time of the order of1 to 8 milliseconds after appearance of a carrier signal. At the end ofthis time interval, under normal operating conditions, the frequencymodulated transmitter 25 will be operating at its centerfrequency. Thesignal applied over conductor 118 is essentially a 60 cycle voltagesignal where the current flow in the conductor 10 is a 60 cyclealternating current. However, the magnitude of this signal is relativelyweak. Accordngly, it is amplified by the output amplifier 52 afterpassing through the low pass filter 51. The low pass filter 51 isapplied where the noise output due to internally generated receivernoise and ambient station impulse noise are limited only by the RFcircuits in the receiver 43. Noise pulses, there fore, retain most ofthis high frequency energy and allow more efiicient filtering action bythe low pass filter 51. The output amplifier 52 may have a relativelylow upper cutoi frequency and tend to spread the noise pulses.Therefore, filtering before amplification is desirable. For relaying alow pass filter having minimum delay and phase shift is used. Formetering applications, a narrow 60 cycle bandpass filter can be used toeliminate all noise components.

The output of the amplifier 52 is applied to a primary Winding 124 of anoutput transformer 125 which has a secondary winding 126 that isconnected to relays or the amplifier 18, FIG. 9, or to other burden asmay be desired. The output amplifier 52 has a frequency responseadequate to pass the direct current component of an assymetrical faultcurrent.

If the impedance of a current responsive burden to Which the output ofthe receiver 43 is applied varies over a wide range and where a greaterpower output is required, the output from the output amplifier 52 can beapplied to the transconductance feedback amplifier 18 shown in FIG. 9.As pointed out hereinbefore the feedback amplifier 18 at the outputterminals 131 and 132 provides an output current that is proportional tothe input voltage from the output amplifier 52 regardless of theimpedance of the metering and/or relaying circuits within the limits ofthe design of the amplifier 18.

The power output of the transconductance feedback amplifier 18 isadequate to drive a variety of solid state relays or conventionalindicating or recording instruments. It is nherently linear and stabledue to its feedback design and connections over its entire operatingrange. Over a more limited range accuracy required for metering can beobtained. This performance is maintained over typical ambienttemperature extremes.

While the transconductance feedback amplifier 18 is normally designedfor a specific impedance range for the metering and/ or relayingcircuits, it operates essentially as a current transformer with respectto the short circuiting of its output terminals. Also, it can be opencircuited without damage to the amplifier and connected equipment orpersonnel.

The amplifier 18 is provided with decoupling and isolating circuitswhich permit the output to be substantially independent of the powersupply voltage. Supply voltage is provided by a battery, the outputvoltage of Which is subject to the usual long term variatons, transientdisturbances, and charger ripple fluctuations. Typical slow or suddenchanges in the voltage from the supply battery produce no change inoutput of the amplifier 18 due to these changes.

The transconductance amplifier 18, providing a current output, is usedonly when current responsive loads or output devices are used. When avoltage responsive device is used, a voltage source must be used. Outputvoltage must remain fixed as load impedance varies up to the rated poweroutput of the amplifier. This requires a low dynamic output impedancewhich generally can be accomplished by strong, negative voltagefeedback. Linearity, stability, accuracy, and power supply currentrequirements are similar to those for the transconductance amplifier 18.

What is claimed as new is:

l. Means for transmitting a signal corresponding to the magnitude of avariable at the potential of a high voltage conductor and for receivingsaid signal at a remote point at ground potential comprising:

(a) a radio transmitter adapted to operate at the potential of saidconductor and to be modulated by said variable to transmit said signal,

(b) a radio receiver at said remote point responsive to said signal fromsaid transmitter to provide an output corresponding to said variable,

(c) said transmitter including means normally nonconducting and renderedconducting when said variable reaches a predetermined value to causesaid transmitter to transmit to said receiver,

(d) means responsive to the output of said receiver,

and

(e) said receiver including means normally non-conducting and renderedconducting a predetermined time after application of said signal to saidreceiver to apply said output to said output responsive means.

2. The invention, as set forth in claim 1, wherein the normallynon-conducting means in the receiver comprises a squelch circuit that isoperable only when the transmitter operates substantially at its normalfrequency and output.

3. The invention, as set forth in claim 1, wherein (a) the transmitterand receiver are frequency modulated, and

(b) the normally non-conducting means in the receiver comprises asquelch circuit that is operable only when said transmitter operatessubstantially at its center frequency.

4. The invention, as set forth in claim 1, wherein the normallynon-conducting means of the transmitter comprises a relay havingnormally open contacts arranged to be closed when the variable reaches apredetermined value to complete an energizing circuit for thetransmitter.

S. Means for transmitting a signal corresponding to the magnitude of avariable at the potential of a high voltage current carrying electricpower transmission conductor and for receiving said signal at a remotepoint at ground potential comprsing:

(a) a radio transmitter adapted to operate at the potential of saidconductor and to be modulated by said variable to transmit said signal,

(b) a radio receiver at said remote point responsive to said signal fromsaid transmitter to provide an output corresponding to said variable,

(e) said transmitter including means normally nonconducting and renderedconducting when said variable reaches a predetermined value to causesaid transmitter to transmit to said receiver,

(d) means responsive to the output of said radio receiver, and

(e) said receiver including means operated a predetermined time afterapplication of said signal to said receiver to apply said output to saidoutput responsive means.

6. Means for transmitting a signal corresponding to the magnitude of avariable at the potential of a high voltage current carrying electricpower transmission conductor and for receiving said signal at a remotepoint at ground potential comprising:

(a) a radio transmitter adapted to operate at the potential of saidconductor and to be modulated by said variable to transmitsad signal,

(b) a radio receiver at said remote point responsive to said signal fromsaid transmitter to provide an output corresponding to said Variable,

(e) means for deriving from said current in said conductor a voltage forapplication to said transmitter for energizing it,

(d) means responsive to said derived voltage for operatively connectingsaid transmitter for energization only when said voltage is at apredetermined value,

(e) means responsive to the output of said radio receiver, and

(f) said receiver including means operated a predetermined time afterapplication of said signal to said receiver to apply said output to saidoutput respon sive means.

7. The nvention, as set forth in claim 6, wherein:

(a) the transmitter is energized by direct current, and

(b) regulating means maintains the voltage of said direct current at asubstantially constant value.

8. The invention, as set forth in claim 6, wherein:

(a) alternating current flows in the conductor,

(b) an alternating voltage is derived from said alternating current,

(e) rectifying and filtering means convert said alternating voltage to adirect voltage substantially free of ripple, and

(d) regulating means maintains said direct voltage at a substantiallyconstant value for energizing the transmitter.

9. The invention, as set forth in claim 8, wherein the transmitter ischaracterized by reaching its normal frequency and output within a-relatively short time with respect to the rate of change of thevariable.

10. The invention, as set forth in claim 8, wherein:

(a) the transmitter and receiver are frequency modulated, and

(b) said transmitter is characterized by reaching its normal frequencyand output within a relatively short time with respect to the rate ofchange of the variable.

11. The invention, as set forth in claim 8, wherein:

(a) the transmitter and receiver are crystal controlled,

and

(b) said receiver is characterized by being tunable over a narrowfrequency range.

12. The invention, as set frth in claim 11, wherein the transmitter andreceiver are fiequency modulated.

13. The invention, as set forth in claim 8, wherein the receiverincludes:

(a) intermediate frequency amplifier and limiter means,

and

(b) noise suppression means comprising:

(l) input band pass filter means to said amplifier and limiter means,

(2) output band pass filter means from said amplifier and limiter means,and

(3) low pass filter means in the output of said receiver.

14. The inventon, as set forth in claim 13, wherein the transmitter andreceiver are frequency modulated.

15. The invention, as set forth in claim 13, wherein the means operateda predetermined time after application of the signal to the receiverincludes squelch circuit means having contacts for completing a circuitto the receiver output.

16. Means for transmitting to a remote point a signal corresponding tothe magnitude of a variable at the potential of a high voltage currentcarrying electric power transmission line conductor comprising:

(a) a tubular conductor for connection in series with said conductor forflow therethrough of line current,

(-b) a radio transmitter within said tubular conductor whereby it isshielded from the electro-magnetic field generated by current flow insaid conductor,

(e) means for energizing said transmitter, and

(d) means for modulating said transmitter in accordance with saidvariable.

17. The invention, as set forth in claim 16, wherein end caps arepositioned at the ends of the tubular conductor, act as a tuned antennafor the transmitter, together with said tubular conductor provideelectrostatic shielding for the transmitter, and are of non-coronaemitting shape.

18. The invention, as set forth in claim 16, wherein:

(a) an outer tubular conductor is concentric and coextensive with thetubular conductor, and

(b) means interconnect said tubular conductors at one end and they areinterposed, in series With the line conductor at their other endswhereby line current flows in opposite directions in said tubular conductors parallel to the axis thereof to neutralize the electromagneticfields generated by current flow through said conductors, to provide anoninductive current carrying structure, and to shield the transmitterfrom external electromagnetic fields.

19. The -invention, as set forth in claim 18, wherein a voltage dropalong at least one of said conductors instananeously proportional tocurrent flow therethrough is the variable for modulating thetransmitter.

20. The invention, as set forth in claim 18, wherein one of said tubularconductors is formed of relatively high resistivity material the voltagedrop along Which is instantaneously proportional to the current flowtherethrough and constitutes the variable to modulate the transmitter.

21. Means for transmitting a signal corresponding to the magnitude of avariable at the potential of a high voltage conductor and for receivingsaid signal at a remote point at ground potential oomprising:

(a) a tubular conductor for connection in series with said conductor forflow therethrough of line current,

(b) a radio transmitter within said tubular conductor whereby it isshielded from the electromagnetic field generated by current flow insaid conductor,

(e) means for energizing said transmitter,

(d) means for modulating said transmitter in accordance With saidvariable,

(e) a radio receiver at said remote point responsive to said signal fromsaid transmitter to provide an output corresponding to said variable,

(f) said transmitter including means normally conconducting and renderedconducting when said Variable reaches a predetermined value to causesaid transm-itter to transmit to said receiver,

(g) means responsive to the output of said receiver,

and

(h) said receiver including means normally non-conducting and renderedconducting a predetermined time after application of said signal to saidreceiver to apply said output to said output responsive means.

References Cited UNITED STATES PATENTS Cook 340--310 Schweitzer 325 67XR Schweitzer 340-310 XR Schweitzer 340-224 XR Induni 325145 XR RICHARDMURRAY, Primary Examiner

